An Overview of Ex nR (Restricted Breathing) Testing and Enclosures

Ex nR (restricted breathing) is a specialised method of explosion protection for electrical equipment used in hazardous environments, particularly Zone 2 areas. Zone 2 environments are locations where explosive gas atmospheres are unlikely to occur during normal operation but could exist for brief periods during fault conditions. Here’s a detailed look at the principles, construction, testing, and applications of Ex nR enclosures.

Purpose of Ex nR Enclosures

Ex nR enclosures are designed to restrict the entry of flammable gases into the equipment they protect, reducing the possibility of an explosive mixture forming inside. The restricted breathing concept aims to restrict gases, vapours and mist from entering while allowing uncertified internal components to operate safely, as long as all external parts meet certification requirements​.

Operating Principle

Unlike other protection methods, such as Ex d (flameproof), which allows for internal explosions to be contained, or Ex e (increased safety), which prevents sparking, Ex nR primarily focuses on reducing the rate at which fuel (flammable gases) enters the enclosure. The enclosure acts as a barrier, limiting gas entry by maintaining a high level of sealing, thereby protecting internal components that may spark or generate heat​.

Construction Features

The construction of Ex nR enclosures typically includes:

• Good Sealing Levels: Gaskets and suitable cable glands are used to create a tight seal to prevent gas ingress.
• Material Composition: Enclosures are often built using lightweight metals like Aluminium, stainless steel sheet, or glass-reinforced polyester (GRP). This ensures durability and corrosion resistance, particularly in harsh environments​.
• Test Ports: Many Ex nR enclosures include a test port to allow for routine checking of the breathing properties during periodic testing​.
• Equipment with High Temperatures or Sparking Potential: These enclosures often house equipment that could pose ignition risks, making the need for restrictive breathing crucial.

Testing and Certification

Ex nR enclosures are subject to rigorous testing to ensure that their restricted breathing properties remain effective over time. Key aspects of the testing process include:

• Pressure Tests: These are conducted to check the enclosure’s ability to maintain its restricted breathing properties under specific conditions. The enclosure is pressurised, and the rate at which pressure decreases is measured to ensure that the seal remains intact​.
• Surface Temperature Test: The enclosure surface temperature is tested at maximum internal power dissipation, to ensure its surface temperature, does not exceed 20K above maximum rated ambient.
• Cable Gland Certification: Glands used with Ex nR enclosures must be certified to ensure they maintain the restrictive properties necessary to restrict gas entry.

Applications in Industry

Ex nR enclosures are widely used in various industries where potentially explosive atmospheres are present.

Key industries include:

• Oil and Gas: Ex nR enclosures are used to protect electrical equipment in refineries, offshore platforms, and processing facilities​.
• Chemical and Pharmaceutical: These industries benefit from Ex nR enclosures for housing sensitive control equipment and instrumentation in potentially explosive areas​.
• Utilities and Renewable Energy: Ex nR enclosures are utilised in biomass plants, power stations and water industry, where they house monitoring and control systems.

Maintenance and Safety Considerations

Maintaining Ex nR enclosures with test port involves routine pressure tests and inspections, typically performed at intervals of six month or more as experience dictates. These enclosures should only be opened under exceptional circumstances to maintain the integrity of their restrictive breathing properties. Competent personnel must carry out these inspections to ensure that the equipment continues to meet IEC 60079-15 and and IEC 60079-17 standards​. 

Should there be a need to open an Ex nR panel outwith the periodic testing time, then the panel must be tested after re-instatement because the seal will have been broken.

Advantages and Flexibility

Ex nR enclosures offer several advantages over other explosion protection methods:

• Cost-Effective and Lightweight: Compared to Ex d enclosures, which are heavier and more expensive, Ex nR enclosures are easier to install and maintain.
• Flexibility in Equipment: By allowing uncertified internal components, Ex nR enclosures provide more flexibility in equipment selection, while still ensuring safety as long as the enclosure itself is properly sealed and certified​.

Conclusion

Ex nR enclosures provide a flexible, lightweight, and cost-effective method for protecting electrical equipment in Zone 2 hazardous environments. Through rigorous sealing and pressure testing, they ensure that flammable gases, vapours and mists are restricted, reducing the risk of explosions. This protection method is critical in industries like oil and gas, chemicals, and renewable energy, where safety and reliability are paramount.​​​​​

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